In a high-frequency amplifier circuit for amplifying incoming burst signals, if power consumption of the amplifier circuit, especially, a field-effect transistor (FET) used as an amplifying element, can be suppressed between bursts when no signal is present and amplification is therefore not necessary, the power consumption of the circuit as a whole can be drastically reduced.
In view of this, Japanese Unexamined Patent Publication No. H05-347514 describes a method in which the presence or absence of a signal is detected at the input of the amplifier circuit and, if no signal is detected, the bias to the gate terminal of the FET is set deeper to reduce power consumption.
However, the method of detecting the presence or absence of a signal at the input of the amplifier circuit involves the problem that the presence or absence of a signal cannot be detected properly if the signal to be detected is very weak.
A high-frequency amplifier circuit having a function for canceling distortion by feedback (a distortion feedback-type amplifier circuit) is described, for example, in Japanese Unexamined Patent Publication No. H05-167356 or 2001-358540. In this type of amplifier circuit, a distortion component is generated by combining a portion of the input to the main amplifier and a portion of the output in opposite phase and equal amplitude relative to the main signal (a distortion extracting circuit), and the distortion component is fed back to the input of the main amplifier in a negative feedback loop (an inverse distortion adding circuit), to achieve a distortion-free amplification.
In the distortion feedback-type amplifier circuit, it is desired that the phase and the power level be preadjustable in the distortion extracting circuit and the inverse distortion adding circuit.
It is also known to provide a high-frequency amplifier circuit having a function for canceling distortion through feedforward control (a feedforward-type amplifier circuit). In the feedforward-type amplifier circuit, as the main amplifier and the auxiliary amplifier for amplifying the distortion component are used in parallel, the characteristics of each individual amplifier, once mounted, cannot be measured. This is also true of an adaptive-type amplifier array or a phased-array type amplifier in which a plurality of amplifiers are used in parallel; that is, the characteristics of each individual amplifier, once mounted, cannot be measured. Therefore, for this type of circuit, it is desired to enable the characteristics of each individual amplifier to be measured even after mounting.